feat(youtube): queue media for background cache and fill fields when rea

- Add `youtube.mediaCache.maxHeight` config option (default 720p)
- Background mode creates text-only cards while cache downloads, queues media updates, fills audio/image fields once cached file is ready
- Announce cache download start and readiness via overlay/OSD notifications
- Skip mpv stream indexes when generating audio from a YouTube cached file

src/core/services/anki-jimaku.ts

@@ -44,6 +44,7 @@ export interface AnkiJimakuIpcRuntimeOptions {
     currentVideoPath: string,
     kind: 'audio' | 'video',
   ) => Promise<string | null>;
+  shouldRequireRemoteMediaCache?: () => boolean;
   showDesktopNotification: (title: string, options: { body?: string; icon?: string }) => void;
   showOverlayNotification?: (payload: OverlayNotificationPayload) => void;
   createFieldGroupingCallback: () => (
@@ -112,6 +113,7 @@ export function registerAnkiJimakuIpcRuntime(
           undefined,
           options.showOverlayNotification,
           options.getCachedMediaPath,
+          options.shouldRequireRemoteMediaCache,
         );
         integration.start();
         options.setAnkiIntegration(integration);